In three previous posts (part 1, part 2 & part 3) I summarized the key highlights of the history of life on Earth, beginning with the Earth’s creation (hint, not by God), and ending with humans’ inventing the radio. I described the most important events, but I didn’t spend any time looking at their implications, particularly what this means for the search for alien life.

What can the history of life on Earth can tell us life on other planets?

Well I’d say it could teach us two major things:

1. Life may be common in the Universe, particularly on planets like the Earth

The fossil and biological evidence suggests that life likely emerged quickly on the Earth. In the first post in the series I put this at 3.8 billion years ago or at 04:00 on the 24-hour clock (if we say that the Earth has existed for 24-hours). This is perhaps a relatively conservative estimate, and some scientists believe life appeared even earlier. Whatever the exact time, it seems that life emerged on Earth almost as soon as the Earth could support it. Before this time asteroids and comets were bombarding the Earth frequently, and much of its surface was volcanic. Life may have tried to get started but was likely quickly annihilated by these hostile conditions.

If life appeared on Earth as soon as it could have, then this may indicate that life is very likely to develop in other locations too, if the conditions are suitable i.e. a supply of carbon, energy and liquid water. Carbon and the other key elements are relatively common in the Universe, and stars’ provide energy, thus if planets like Earth exist at the right distance from their stars, they may well have life. A great way to test this hypothesis is by looking for evidence of life on Mars, as early in its history the red planet was probably similar to Earth, with an atmosphere, a warmer climate and even surface liquid water. Mars is currently being studied by NASA and ESA, fingers crossed they find some fossils!

2. Intelligent life may not be very common in the Universe, particularly life capable of interstellar communication

Although life appeared on Earth relatively quickly, intelligent life in the form of human beings took a very long time to evolve. If we use the 24-hour clock analogy, life first emerged at 04:00 but human beings didn’t emerge until, 23:59:56, we’ve only been around for roughly 4 seconds!

It gets worse for the alien hunters. Life on Earth remained single celled (like bacteria) for well over half of its history, from 04:00 to 17:40 on the 24-hour clock, at which point the first multicellular life emerged. The first true animals didn’t emerge until 20:56 in the Earth’s evening, and the first four legged land animals didn’t appear until 21:55. The kind of advanced life we take for granted today evolved relatively late in the Earth’s history. So does this mean that advanced life will probably emerge on other Earth-like planets, but will take a long time about it?

Maybe not, it gets even worse. Geological evidence suggests that many of the key steps in the evolution of life happened after enormous extinctions. Multicellular life and true animals may both have evolved after incidents in which the entire Earth froze over like a giant snowball, mammals didn’t evolve until after potentially the greatest of mass extinctions (the Permian mass extinction), and remained as little more than small rodents for hundreds of millions of years until a chance meteorite strike wiped-out the dinosaurs. This suggests that evolution does not inevitably lead to intelligent life, evolution may require regular extreme-shocks to move it along. Think about it, humans probably wouldn’t exist if the dinosaurs hadn’t gone extinct.

All this means that just because life can become complex and intelligent doesn’t mean that it necessarily will do. If many Earth-like planets don’t receive the right fortuitous sequence of catastrophes’, then maybe life will remain relatively simple for the whole of a planet’s existence.

And it gets even worse for the search for intelligent aliens. Humans’ have only been around for an incredibly short time, and we’ve only had the radio for little over a century, a few tens of thousands of seconds of the 24-hours of Earth’s existence. Furthermore we don’t know how long we’ll be around for. We tend to think of ourselves as masters of the Earth, we’re intelligent, we can build cars and iphones, and we can change the world around us to better suit our needs. But we also have the capability to destroy most life on Earth, and we don’t really know how well our civilisation can withstand the worst that the Earth has to throw at us. I guess we’ll get a taster with climate change. Who knows how long we’ll be around before we go extinct? (All species go extinct eventually). Maybe we’ll be short-lived species?

So, to sum up, although life may be common in our Galaxy, intelligent life capable of receiving and sending radio waves may be very rare, and may only exist for a short-time before it, or something else, destroys it.

Earlier I wrote about the Drake Equation, which is an attempt to predict the number of advanced civilizations in our galaxy, and about the Fermi Paradox, which asks why haven’t we found intelligent life in the Milky Way if there are so many places in which life can evolve and so much time? We don’t know the answer to either, but I think this is a pretty good explanation; there may be loads of alien life, it just can’t use a radio.

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7 Responses to “Why the Universe may be full of life, but not intelligent life”

I really enjoyed reading this, as these are points I bring up all the time when my supposedly enlightened friends get on the universe is full of life kick. I’d even go one step further stating that finding a planet that is connected to a planetoid in the right distance with all the right chemical components would be exremely rare. Even given the vastness of space. Hell, there could be a million worlds out there that only evolved as far as insect and plant life, and never needing to go beyond that, didn’t. I am in complete aggreement that without mass exstinction events in earth’s history, half of the more intelligent species would never have appeard. Great post and keep it up!

Spot on, there is no reason for any creature to modify or manipulate the EM spectrum. Generally, the life on earth, until recently, followed the big 3. Rate of reproduction, Rate/efficiency of energy conversion, Durability/Survivability. Intelligence can assist this, but higher birth rates, easy of acquiring food, and how long you can go without eating and survive, have more to do with a species success than intelligence. Personally, I do not think it is intelligence, but curiosity that is the core evolutionary step. Many mammals are curious but only the prime ape show a real inquisitive nature. In addition, this did not occur until world ending events and the climate really stabilized much more than in the past. Will we live forever, hell no, but we have covered so much ground in the last 400 years who know were we will be in 400 more. (About 2.4 millionth of a second in your 24-hour analogy.)

Great article – and spot on with much of what I’ve tried to tell both Flat-Earthers who say life is impossible in the universe, and disappointed Trekkies who are baffled that aliens haven’t contacted us already.

I’d add that the “intelligence” of intelligent life itself is very likely an interesting problem: I’ve seen fairly sound-looking research that suggests that the relatively large brain size of human beings is intimately tied to handling social interaction with other humans – or, to put it another way, the brain-size of primates predicts the size of the troupe it is able to comfortably live in, more than its intelligence.

I think one conclusion we might fairly take from this is that Intelligent life as humans understand it is very likely an accidental side-effect of a far more important factor for survival, more than it is an inevitable result of evolution. Intelligence may not play a particularly important part in the long-term survival of a species, it might arguably be counter-productive to long-term survival, and most importantly it may be an accidental side-effect that is unlikely to occur anywhere in the universe.

In some ways, it might even be argued that intelligence is a sort of mental disorder, a disconnection from reality: a normal, sane animal looks at a stick and fairly accurately determines whether the stick is threat or not-threat and then food or not-food, while an abnormal animal looks at the same stick and thinks the insane thought of “that’s kind of like a wooden fist at the end of a long wooden arm, and with a long wooden fist like that I can beat stuff up!” It could only be some form of obsessive disorder that drives an animal to compose classical music, invent language, write down history, imagine gods and try to figure out how many angels dance on the head of a pin, trade gold for food or water or reproduction or to hire warriors or pay off tyrants or buy paintings or invent insurance or investments. It’s a freakish madness that can cause a land-based temperate animal to look at deserts, arctic wastelands, oceans, and the moon, and say “I can live there, and there, and there, and there – I can live ANYWHERE!” And then, there’s the insanity of the bewildering variety of ways an intelligent animal can play with fire, until it straps itself into a rocket and fires itself into the stars. What is normal and sane about the invention of nuclear reactors and weapons, or about using invisible forms of light to “talk” to each other in a kind of artificial telepathy, or to use microwaves to cook or communicate, lasers to communicate or make weapons or perform surgery, and so on?

The search for intelligent life is a search for animals that have malfunctioned as bizarrely as human beings have!

So, I have every reason to believe that life is at least somewhat common in the universe, but I have no reason to think that intelligent life is equally common – in fact, just the opposite: intelligent life looks to me like a bizarre joke played by chance in life on Earth, and one that must surely be unlikely to be repeated just anywhere else.

Earth is a habitable planet but it is not what is now called by astrobiologists a super-habitable planet. Super-habitable planets would have better conditions more suitable to the continued evolution of intelligent life. For example the asteroids that bombard earth are the remains of a destroyed planet….other solar system may not have this problem. They also may not have super-volcanos, snow-ball earth ice ages or other natural catastrophes. A planet circling a dwarf star may last 10 billion years in a
habitable zone In fifty years using earth as the best model for evolving intelligent life will be flat earth thinking as will be your article.